Commercial and entertainment lighting applications such as lighting for advertisements, disco lighting, theater lighting, stage lighting, traffic lighting, etc. often times require light to be emitted with high color saturation for optimal presentation. Typically, high color saturation is generated by applying a narrow selective filter to an incandescent light source. The light source generates white light, which comprises a combination of light with different wavelengths in the visible spectrum. The filter selectively filters the white light to provide the desired color light emission. The color pigments, dyes, or colorants, used in these filters are typically transparent color filters which absorb the unwanted color light. While this system generates highly saturated color light, it also wastes a significant portion of the light generated by the light source, as a significant portion is absorbed by the selective filter rather than being transmitted.
White light emitting diodes (LEDs) are known in the art and are a relatively recent innovation. It was not until LEDs emitting the blue/ultraviolet of the electromagnetic spectrum were developed that it became practical to develop white light sources based on LEDs. As is known white light generating LEDs (“white LEDs”) include photo-luminescent materials (e.g., one or more phosphor materials), which absorbs a portion of the radiation emitted by the LED and re-emits radiation of a different color (e.g., range of wavelengths). For example, the LED emits blue light in the visible part of the spectrum and the phosphor re-emits yellow or a combination of green and red light, green and yellow, or yellow and red light. The portion of the visible blue light emitted by the LED which is not absorbed by the phosphor mixes with the yellow light emitted to provide light which appears to the eye as being white. In addition to generating white light, the combination of an LED and photo-luminescent material may be configured to generate any number of colors in the visible spectrum.
This provides much more efficient use of the LED light source, as a significant amount of light generated by the LED light source is transmitted or absorbed and re-emitted by the photo-luminescent material.
However, a problem that arises is that although a photo-luminescent material may create sufficient light in the target color wavelength, this is typically a much broader emission curve than desired for high color saturation. This may be particularly problematic for certain type of lighting that require high color saturation, such as lighting for advertisements, disco lighting, theater lighting, stage lighting, traffic lighting.
Therefore, there is a need for an improved approach to improve the color characteristics for LED lighting devices.